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I n t e r n a t i o n a l T e l e c o m m u n i c a t i o n U n i o n

ITU-T G.654TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU

(10/2012)

SERIES G: TRANSMISSION SYSTEMS AND MEDIA,DIGITAL SYSTEMS AND NETWORKS

Transmission media and optical systems characteristics –Optical fibre cables

Characteristics of a cut-off shifted single-modeoptical fibre and cable

Recommendation ITU-T G.654

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ITU-T G-SERIES RECOMMENDATIONS

TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS

INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS G.100–G.199

GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER-TRANSMISSION SYSTEMS

G.200–G.299

INDIVIDUAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONESYSTEMS ON METALLIC LINES G.300–G.399

GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMSON RADIO-RELAY OR SATELLITE LINKS AND INTERCONNECTION WITH METALLICLINES

G.400–G.449

COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY G.450–G.499

TRANSMISSION MEDIA AND OPTICAL SYSTEMS CHARACTERISTICS G.600–G.699

General G.600–G.609

Symmetric cable pairs G.610–G.619

Land coaxial cable pairs G.620–G.629

Submarine cables G.630–G.639

Free space optical systems G.640–G.649

Optical fibre cables G.650–G.659

Characteristics of optical components and subsystems G.660–G.679Characteristics of optical systems G.680–G.699

DIGITAL TERMINAL EQUIPMENTS G.700–G.799

DIGITAL NETWORKS G.800–G.899

DIGITAL SECTIONS AND DIGITAL LINE SYSTEM G.900–G.999

MULTIMEDIA QUALITY OF SERVICE AND PERFORMANCE – GENERIC AND USER-RELATED ASPECTS

G.1000–G.1999

TRANSMISSION MEDIA CHARACTERISTICS G.6000–G.6999

DATA OVER TRANSPORT – GENERIC ASPECTS G.7000–G.7999

PACKET OVER TRANSPORT ASPECTS G.8000–G.8999

ACCESS NETWORKS G.9000–G.9999

For further details, please refer to the list of ITU-T Recommendations.

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ii Rec. ITU-T G.654 (10/2012)

FOREWORD

The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of

telecommunications, information and communication technologies (ICTs). The ITU Telecommunication

Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical,

operating and tariff questions and issuing Recommendations on them with a view to standardizingtelecommunications on a worldwide basis.

The World Telecommunication Standardization Assembly (WTSA), which meets every four years,

establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on

these topics.

The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1.

In some areas of information technology which fall within ITU-T's purview, the necessary standards are

prepared on a collaborative basis with ISO and IEC.

NOTE

In this Recommendation, the expression "Administration" is used for conciseness to indicate both a

telecommunication administration and a recognized operating agency.

Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain

mandatory provisions (to ensure, e.g., interoperability or applicability) and compliance with the

Recommendation is achieved when all of these mandatory provisions are met. The words "shall" or some

other obligatory language such as "must" and the negative equivalents are used to express requirements. The

use of such words does not suggest that compliance with the Recommendation is required of any party.

INTELLECTUAL PROPERTY RIGHTS

ITU draws attention to the possibility that the practice or implementation of this Recommendation may

involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence,

validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others

outside of the Recommendation development process.

As of the date of approval of this Recommendation, ITU had received notice of intellectual property,

protected by patents, which may be required to implement this Recommendation. However, implementers

are cautioned that this may not represent the latest information and are therefore strongly urged to consult the

TSB patent database at http://www.itu.int/ITU-T/ipr/.

ITU 2013

All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the

prior written permission of ITU.

http://www.itu.int/ITU-T/ipr/



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Rec. ITU-T G.654 (10/2012) iii

Table of Contents

Page

1

Scope ............................................................................................................................ 1

2

References..................................................................................................................... 2

3

Definitions .................................................................................................................... 2

4

Abbreviations and acronyms ........................................................................................ 2

5

Fibre attributes .............................................................................................................. 3

5.1

Mode field diameter ....................................................................................... 3

5.2

Cladding diameter .......................................................................................... 3

5.3

Core concentricity error .................................................................................. 3

5.4

Non-circularity ............................................................................................... 3

5.5

Cut-off wavelength ......................................................................................... 3

5.6

Macrobending loss .......................................................................................... 4

5.7

Material properties of the fibre ....................................................................... 4

5.8

Refractive index profile .................................................................................. 5

5.9

Longitudinal uniformity of chromatic dispersion ........................................... 5

5.10

Chromatic dispersion coefficient .................................................................... 5

6

Cable attributes ............................................................................................................. 5

6.1

Attenuation coefficient ................................................................................... 5

6.2

Polarization mode dispersion (PMD) coefficient ........................................... 6

7

Tables of recommended values .................................................................................... 6

Appendix I – Information for link attributes and system design ............................................. 11

I.1

Attenuation ..................................................................................................... 11

I.2

Chromatic dispersion ...................................................................................... 11

I.3

Differential group delay (DGD) ..................................................................... 12

I.4

Non-linear coefficient ..................................................................................... 12

I.5

Tables of common typical values ................................................................... 12

Bibliography............................................................................................................................. 14

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Rec. ITU-T G.654 (10/2012) 1

Recommendation ITU-T G.654

Characteristics of a cut-off shifted single-mode optical fibre and cable

1 Scope

This Recommendation describes a single-mode optical fibre and cable which has thezero-dispersion wavelength around 1300 nm wavelength, which is loss-minimized and cut-off

shifted at a wavelength around 1550 nm, and which is optimized for use in the 1530-1625 nm

region.

This very low loss cut-off shifted fibre (CSF) can be used for long-distance digital transmission

applications such as long-haul terrestrial line systems and submarine cable systems using optical

amplifiers. The geometrical, optical (attenuation, cut-off wavelength, chromatic dispersion and

polarization mode dispersion, etc.), transmission and mechanical characteristics of this CSF are

described below.

Some provisions are made to support transmission at higher wavelengths up to 1625 nm. The

geometrical, optical, transmission and mechanical parameters are described below in three

categories of attributes:

• fibre attributes are those attributes that are retained throughout cabling and installation;

• cable attributes that are recommended for cables as they are delivered;

• link attributes that are characteristics of concatenated cables, describing estimation methods

of system interface parameters based on measurements, modelling, or other considerations.

Information for link attributes and system design are given in Appendix I.

This Recommendation, and the different performance categories found in the tables of clause 7, are

intended to support the following related-system Recommendations:

• [b-ITU-T G.957];

• [b-ITU-T G.691];

• [b-ITU-T G.692];

• [b-ITU-T G.959.1];

• [b-ITU-T G.973];

• [b-ITU-T G.973.1];

• [b-ITU-T G.973.2];

• [b-ITU-T G.977].

The meaning of the terms used in this Recommendation, and the guidelines to be followed in themeasurements to verify the various characteristics, are given in [ITU-T G.650.1] and

[ITU-T G.650.2]. The characteristics of this fibre, including the definitions of the relevant

parameters, their test methods and relevant values, will be refined as studies and experience

progress.

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2 Rec. ITU-T G.654 (10/2012)

2 References

The following ITU-T Recommendations and other references contain provisions which, through

reference in this text, constitute provisions of this Recommendation. At the time of publication, the

editions indicated were valid. All Recommendations and other references are subject to revision;

users of this Recommendation are therefore encouraged to investigate the possibility of applying the

most recent edition of the Recommendations and other references listed below. A list of the

currently valid ITU-T Recommendations is regularly published. The reference to a document withinthis Recommendation does not give it, as a stand-alone document, the status of a Recommendation.

[ITU-T G.650.1] Recommendation ITU-T G.650.1 (2010), Definitions and test methods for

linear, deterministic attributes of single-mode fibre and cable.

[ITU-T G.650.2] Recommendation ITU-T G.650.2 (2007), Definitions and test methods for

statistical and non-linear related attributes of single-mode fibre and cable.

3 Definitions

For the purposes of this Recommendation, the definitions given in [ITU-T G.650.1] and

[ITU-T G.650.2] apply.

Values shall be rounded to the number of digits given in the table of recommended values before

conformance is evaluated.

4 Abbreviations and acronyms

This Recommendation uses the following abbreviations and acronyms:

CSF Cut-off Shifted Fibre

DGD Differential Group Delay

DWDM Dense Wavelength Division MultiplexingMFD Mode Field Diameter

OSNR Optical Signal to Noise Ratio

PMD Polarization Mode Dispersion

PMDQ Statistical parameter for PMD link

RTM Reference Test Method

TBD To Be Determined

WDM Wavelength Division Multiplexing

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Rec. ITU-T G.654 (10/2012) 3

5 Fibre attributes

Only those characteristics of the fibre providing a minimum essential design framework for fibre

manufacturers are recommended in this clause. Ranges or limits on values are presented in the

tables of clause 7. Of these, cable manufacture or installation may significantly affect the cabled

fibre cut-off wavelength and polarization mode dispersion (PMD). Otherwise, the recommended

characteristics will apply equally to individual fibres, fibres incorporated into a cable wound on a

drum, and fibres in an installed cable.

5.1 Mode field diameter

Both a nominal value and tolerance about that nominal value of mode field diameter (MFD) shall be

specified at 1550 nm. The nominal values of the MFD that is specified shall be within the range

found in clause 7. The specified tolerance of the MFD shall not exceed the value in clause 7. The

deviation from nominal shall not exceed the specified tolerance.

5.2 Cladding diameter

The recommended nominal value of the cladding diameter is 125 μm.

A tolerance is also specified and shall not exceed the value in clause 7. The cladding deviation from

nominal shall not exceed the specified tolerance.

5.3 Core concentricity error

The core concentricity error shall not exceed the value specified in clause 7.

5.4 Non-circularity

5.4.1 Mode field non-circularity

In practice, the mode field non-circularity of fibres having nominally circular mode fields is found

to be sufficiently low that propagation and jointing are not affected. It is, therefore, not considerednecessary to recommend a particular value for the mode field non-circularity. It is not normally

necessary to measure the mode field non-circularity for acceptance purposes.

5.4.2 Cladding non-circularity

The cladding non-circularity shall not exceed the value found in clause 7.

5.5 Cut-off wavelength

Two useful types of cut-off wavelength can be distinguished:

a) Cable cut-off wavelength, λ cc.

b) Fibre cut-off wavelength, λ c. NOTE 1 – For some specific submarine cable applications, other cable cut-off wavelength values may be

required.

The correlation of the measured values of λ c and λ cc depends on the specific fibre and cable design

and the test conditions. While in general, λ cc < λ c, a general quantitative relationship cannot be

easily established.

The importance of ensuring single-mode transmission in the minimum cable length between joints

at the minimum operating wavelength is paramount. This can be approached in two alternate ways:

1) recommending λc to be less than 1600 nm: when a lower limit is appropriate, λc should be

greater than 1350 nm;2) recommending the maximum value of λ cc to be 1530 nm.

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4 Rec. ITU-T G.654 (10/2012)

NOTE 2 – The above values ensure single-mode transmission at around 1550 nm. For WDM applications

requiring operation at a wavelength of (1550 nm-x), the above values should be reduced by x nm.

These two specifications need not both be invoked. Since specification of λ cc is a more direct way of

ensuring single-mode cable operation, it is the preferred option. When circumstances do not readily

permit the specification of λ cc (e.g., in single-mode optical fibre cables such as jumper cables or

cables to be deployed in a significantly different manner than in the λ cc RTM), then the specification

of λ c is appropriate.

When the user chooses to specify λ cc as in item 2), it should be understood that λ c may exceed

1600 nm.

When the user chooses to specify λ c as in item 1), then λ cc need not be specified.

In the case where the user chooses to specify λ cc, it may be permitted that λ c be higher than the

minimum operating wavelength relying on the effects of cable fabrication and installation to yield

λ cc values below the minimum operating wavelength for the shortest length of cable between two

joints.

In the case where the user chooses to specify λ cc, a qualification test may be sufficient to verify thatthe λ cc requirement is being met.

The cable cut-off wavelength, λ cc, shall not exceed the maximum specified in clause 7.

5.6 Macrobending loss

Macrobending loss varies with wavelength, bend radius and number of turns about a mandrel with a

specified radius. Macrobending loss shall not exceed the maximum given in clause 7 for the

specified wavelength(s), bend radius, and number of turns.

NOTE 1 – A qualification test may be sufficient to ensure that this requirement is being met.

NOTE 2 – The recommended number of turns corresponds to the approximate number of turns deployed in

all splice cases of a typical repeater span. The recommended radius is equivalent to the minimum bend-radius widely accepted for long-term deployment of fibres in practical systems installations to avoid

static-fatigue failure.

NOTE 3 – If, for practical reasons, fewer than the recommended number of turns are chosen for

implementation, it is suggested that not less than 40 turns and a proportionately smaller loss increase be

required.

NOTE 4 – The macrobending loss recommendation relates to the deployment of fibres in practical

single-mode fibre installations. The influence of the stranding-related bending radii of cabled single-mode

fibres on the loss performance is included in the loss specification of the cabled fibre.

NOTE 5 – In the event that routine tests are required, a smaller diameter loop with one or several turns can

be used instead of the recommended test, for accuracy and measurement ease. In this case, the loop diameter,

number of turns, and the maximum permissible bend loss for the several-turn test should be chosen so as to

correlate with the recommended test and allowed loss.

5.7 Material properties of the fibre

5.7.1 Fibre materials

The substances of which the fibres are made should be indicated.

NOTE – Care may be needed in fusion splicing fibres of different substances. Provisional results indicate

that adequate splice loss and strength can be achieved when splicing different high-silica fibres.

5.7.2 Protective materials

The physical and chemical properties of the material used for the fibre primary coating and the best

way of removing it (if necessary) should be indicated. In the case of single-jacketed fibre, similar

indications shall be given.

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Rec. ITU-T G.654 (10/2012) 5

5.7.3 Proofstress level

The specified proofstress, σ p, shall not be less than the minimum specified in clause 7.

NOTE – The definitions of the mechanical parameters are contained in clauses 3.2 and 5.7 of

[ITU-T G.650.1].

5.8 Refractive index profile

The refractive index profile of the fibre does not generally need to be known.

5.9 Longitudinal uniformity of chromatic dispersion

Under study.

NOTE – At a particular wavelength, the local absolute value of the chromatic dispersion coefficient can vary

away from the value measured on a long length. If the value decreases to a small value at a wavelength that

is close to an operating wavelength in a DWDM system, four-wave mixing can induce the propagation of

power at other wavelengths, including, but not limited to, other operating wavelengths. The magnitude of the

four-wave mixing power is a function of the absolute value of the chromatic dispersion coefficient, the

chromatic dispersion slope, the operating wavelengths, the optical power, and the distance over which

four-wave mixing occurs.

For DWDM operations in the 1550 nm region, the chromatic dispersion of ITU-T G.654 fibres is

large enough to avoid four-wave mixing. Chromatic dispersion uniformity is therefore not a

functional issue.

5.10 Chromatic dispersion coefficient

The measured group delay or chromatic dispersion per unit fibre length versus wavelength shall be

fitted by the quadratic equation as defined in Annex A of [ITU-T G.650.1]. (See clause 5.5 of

[ITU-T G.650.1] for guidance on the interpolation of dispersion values to unmeasured

wavelengths.)

Depending on accuracy requirements, for wavelength intervals of up to 35 nm, the quadraticequation is allowed in the 1550 nm region. For longer wavelength intervals, either the 5-term

Sellmeier model or the 4th order polynomial model is recommended. It is not meant to be used in

the 1310 nm region.

NOTE – It is not necessary to measure the chromatic dispersion coefficient on a routine basis.

6 Cable attributes

Since the geometrical and optical characteristics of fibres given in clause 5 are barely affected by

the cabling process, this clause will give recommendations mainly relevant to transmission

characteristics of cabled factory lengths.

Environmental and test conditions are paramount and are described in the guidelines for test

methods.

6.1 Attenuation coefficient

The attenuation coefficient is specified with a maximum value at one or more wavelengths in the

1530-1625 nm region. The optical fibre cable attenuation coefficient values shall not exceed the

values found in clause 7.

NOTE 1 – The lowest values depend on the fabrication process, fibre composition and design, and cable

design.

Values of 0.15 to 0.19 dB/km in the 1550 nm region have been achieved.

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6 Rec. ITU-T G.654 (10/2012)

NOTE 2 – The attenuation coefficient may be calculated across a spectrum’s wavelengths, based on

measurements at a few (3 to 4) predictor wavelengths. This procedure is described in clause 5.4.4 of

[ITU-T G.650.1] and an example for ITU-T G.652 fibre is given in Appendix III of [ITU-T G.650.1].

NOTE 3 – For applications of submarine systems with remotely pumped optical amplifier described in

[b-ITU-T G.973], other attenuation coefficients in the pump wavelength region may be required.

6.2 Polarization mode dispersion (PMD) coefficientCabled fibre polarization mode dispersion shall be specified on a statistical basis, not on an

individual fibre basis. The requirements pertain only to the aspect of the link calculated from cable

information. The metrics of the statistical specification are found below. Methods of calculations

are found in [b-IEC/TR 61282-3], and are summarized in Appendix IV of [ITU-T G.650.2].

The manufacturer shall supply a PMD link design value, PMDQ, that serves as a statistical upper

bound for the PMD coefficient of the concatenated optical fibre cables within a defined possible

link of M cable sections. The upper bound is defined in terms of a small probability level, Q, which

is the probability that a concatenated PMD coefficient value exceeds PMDQ. For the values of M

and Q given in clause 7, the value of PMDQ shall not exceed the maximum PMD coefficient

specified in clause 7.Measurements and specifications on uncabled fibre are necessary, but not sufficient to ensure the

cabled fibre specification. The maximum link design value specified on uncabled fibre shall be less

than or equal to that specified for the cabled fibre. The ratio of PMD values for uncabled fibre to

cabled fibre depends on the details of the cable construction and processing, as well as on the mode

coupling condition of the uncabled fibre. [ITU-T G.650.2] recommends a low mode coupling

deployment requiring a low tension wrap on a large diameter spool for uncabled fibre PMD

measurements.

The limits on the distribution of PMD coefficient values can be interpreted as being nearly

equivalent to limits on the statistical variation of the differential group delay (DGD), that varies

randomly with time and wavelength. When the PMD coefficient distribution is specified for opticalfibre cable, equivalent limits on the variation of DGD can be determined. The metrics and values

for link DGD distribution limits are found in Appendix I.

NOTE 1 – PMDQ should be calculated for various types of cables, and they should usually be calculated

using sampled PMD values. The samples would be taken from cables of similar construction.

NOTE 2 – The PMDQ specification should not be applied to short cables such as jumper cables, indoor

cables and drop cables.

7 Tables of recommended values

The following tables summarize the recommended values for a number of categories of fibres that

satisfy the objectives of this Recommendation. These categories are largely distinguished on the basis of requirements for mode field diameter, chromatic dispersion coefficient and PMD. See

Appendix I for information about transmission distances and bit rates relative to PMD requirements.

Table 1, ITU-T G.654.A Attributes, is the base category for a cut-off shifted single-mode optical

fibre and cable. This category is suitable for the system in [b-ITU-T G.691], [b-ITU-T G.692],

[b-ITU-T G.957] and [b-ITU-T G.977] in the 1550 nm wavelength region.

Table 2, ITU-T G.654.B Attributes, is suitable for the system described in [b-ITU-T G.691],

[b-ITU-T G.692], [b-ITU-T G.957], [b-ITU-T G.977] and [b-ITU-T G.959.1] long-haul application

in the 1550 nm wavelength region. This category can be applied to longer distance and larger

capacity WDM transmission systems, e.g., repeaterless submarine systems with remotely pumped

optical amplifier described in [b-ITU-T G.973] and submarine systems with optical amplifiersdescribed in [b-ITU-T G.977].

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Rec. ITU-T G.654 (10/2012) 7

Table 3, ITU-T G.654.C Attributes, is similar to ITU-T G.654.A, but the reduced PMD requirement

supports higher bit-rate and long-haul applications in [b-ITU-T G.959.1].

Table 4, ITU-T G.654.D Attributes, is similar to ITU-T G.654.B, but has a modified macrobend

loss specification as well as lower attenuation and larger MFD to improve the OSNR

characteristics. This category is recommended for higher bit-rate submarine systems described in

[b-ITU-T G.973], [b-ITU-T G.973.1], [b-ITU-T G.973.2], and [b-ITU-T G.977].

NOTE – ITU-T G.654 fibre with larger MFD than category B for terrestrial use is for further discussion.

Table 1 – ITU-T G.654.A

Fibre attributes

Attribute Detail Value

Mode field diameter Wavelength 1550 nm

Range of nominal values 9.5-10.5 µm

Tolerance ±0.7 µm

Cladding diameter Nominal 125 µm

Tolerance ±1 μm

Core concentricity error Maximum 0.8 μm

Cladding non-circularity Maximum 2.0%

Cable cut-off wavelength Maximum 1530 nm

Macrobend loss Radius 30 mm

Number of turns 100

Maximum at 1625 nm 0.50 dB

Proof stress Minimum 0.69 GPa

Chromatic dispersion coefficient D1550max 20 ps/nm · km

S1550 max 0.070 ps/nm2 · km

Uncabled fibre PMD coefficient Maximum (Note 2)

Cable attributes


Attenuation coefficient

(Note 1)

Maximum at 1550 nm 0.22 dB/km

PMD coefficient

(Note 2)

M 20 cables

Q 0.01%

Maximum PMDQ 0.5 ps/√km

NOTE 1 – The attenuation coefficient values listed in this table should not be applied to short cables such

as jumper cables. For example, [b-IEC 60794-2-11] specifies the attenuation coefficient of indoor cable as

1.0 dB/km or less.

NOTE 2 – According to clause 6.2, a maximum PMDQ value on uncabled fibre is specified in order to

support the primary requirement on cable PMDQ.

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8 Rec. ITU-T G.654 (10/2012)

Table 2 – ITU-T G.654.B

Fibre attributes


Mode field diameter Wavelength 1550 nmRange of nominal values 9.5-13.0 µm

Tolerance ±0.7 µm


Tolerance ±1 μm





Number of turns 100




S1550max 0.070 ps/nm2 · km


Cable attributes



(Note 1)


PMD coefficient

(Note 2)

M 20 cables

Q 0.01%




1.0 dB/km or less.



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Rec. ITU-T G.654 (10/2012) 9

Table 3 – ITU-T G.654.C

Fibre attributes



Tolerance ±0.7 µm


Tolerance ±1 μm





Number of turns 100




S1550max 0.070 ps/nm2 · km


Cable attributes


Attenuation coefficient(Note 1)


PMD coefficient

(Note 2)

M 20 cables

Q 0.01%




1.0 dB/km or less.



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10 Rec. ITU-T G.654 (10/2012)

Table 4 – ITU-T G.654.D

Fibre attributes



Tolerance ±0.7 µm


Tolerance ±1 μm




Macrobend loss

(Note 4)

Radius To be determined

Number of turns To be determined

Maximum at 1550 nm To be determined

Radius 30 mm

Number of turns 100


Proof stress (Note 2) Minimum 0.69 GPa


S1550max 0.070 ps/nm2 · km


Cable attributes



(Note 1)


PMD coefficient

(Note 3)

M 20 cables

Q 0.01%



as jumper cables. For example, [b-IEC 60794-2-11] specifies the attenuation coefficient of indoor cable as1.0 dB/km or less.

NOTE 2 – A higher proof stress may be considered depending on the applied system requirements.



NOTE 4 – Macrobend loss specification at 1550 nm may be useful in some systems. The specification

values are to be determined including bending radius and number of turns.

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Rec. ITU-T G.654 (10/2012) 11

Appendix I

Information for link attributes and system design

(This appendix does not form an integral part of this Recommendation.)

A concatenated link usually includes a number of spliced factory lengths of optical fibre cable. The

requirements for factory lengths are given in clauses 5 and 6. The transmission parameters for

concatenated links must take into account not only the performance of the individual cable lengths

but also the statistics of concatenation.

The transmission characteristics of the factory length optical fibre cables will have a certain

probability distribution which often needs to be taken into account if the most economic designs are

to be obtained. The following clauses should be read with this statistical nature of the various

parameters in mind.

Link attributes are affected by factors other than optical fibre cables; by such things as splices,

connectors and installation. These factors cannot be specified in this Recommendation. For the purpose of estimation of link attribute values, typical values of optical fibre links are provided in

clause I.5. The estimation methods of parameters needed for system design are based on

measurements, modelling or other considerations.

I.1 Attenuation

The attenuation A of a link is given by:

y x L A c s α+α+α= (I-1)

where:

α = typical attenuation coefficient of fibre cables in a link

L = length of a link

αs = mean splice loss

x = number of splices in a link

αc = mean loss of line connectors

y = number of line connectors in a link (if provided)

A suitable margin should be allocated for future modifications of cable configurations (additional

splices, extra cable lengths, ageing effects, temperature variations, etc.). Equation I-1 does not

include the loss of equipment connectors. The typical values found in clause I.5 are for the

attenuation coefficient of an optical fibre link. The attenuation budget used in designing an actual

system should account for the statistical variations in these parameters.

I.2 Chromatic dispersion

The chromatic dispersion in ps/nm can be calculated from the chromatic dispersion coefficients of

the factory lengths, assuming a linear dependence on length, and with due regard for the signs of the

coefficients (see clause 5.10).

When these fibres are used for transmission in the 1550 nm region, some forms of chromatic

dispersion compensation are often employed. In this case, the average link chromatic dispersion is

used for design. The measured dispersion in the 1550 nm window can be characterized within the

1550 nm window by a linear relationship with wavelength. The relationship is described in terms of

the typical chromatic dispersion coefficient and dispersion slope coefficient at 1550 nm.

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12 Rec. ITU-T G.654 (10/2012)

Typical values for the chromatic dispersion coefficient, D1550, and chromatic dispersion slope

coefficient, S1550, at 1550 nm are found in clause I.5. These values, together with link length, Link,

can be used to calculate the typical chromatic dispersion for use in optical link design.

( ) ( )[ ] (ps/nm)155015501550 −λ +=λ S D L D Link Link (I-2)

I.3 Differential group delay (DGD)

The differential group delay (DGD) is the difference in arrival times of the two polarization modes

at a particular wavelength and time. For a link with a specific PMD coefficient, the DGD of the link

varies randomly with time and wavelength as a Maxwell distribution that contains a single

parameter, which is the product of the PMD coefficient of the link and the square root of the link

length. The system impairment due to PMD at a specific time and wavelength depends on the DGD

at that time and wavelength. So, means of establishing useful limits on the DGD distribution as it

relates to the optical fibre cable PMD coefficient distribution and its limits have been developed and

are documented in [b-IEC/TR 61282-3]. The metrics of the limitations of the DGD distribution

follow:

NOTE – The determination of the contribution of components other than optical fibre cable is beyond the

scope of this Recommendation, but is discussed in [b-IEC/TR 61282-3].

Reference link length, LRef : A maximum link length to which the maximum DGD and probability

will apply. For longer link lengths, multiply the maximum DGD by the square root of the ratio of

actual length to the reference length.

Typical maximum cable length, LCab: The maxima are assured when the typical individual cables of

the concatenation or the lengths of the cables that are measured in determining the PMD coefficient

distribution are less than this value.

Maximum DGD, DGDmax: The DGD value that can be used when considering optical system

design.

Maximum probability, PF: The probability that an actual DGD value exceeds DGDmax.

I.4 Non-linear coefficient

The effect of chromatic dispersion is interactive with the non-linear coefficient, n2/Aeff , regarding

system impairments induced by non-linear optical effects (see [b-ITU-T G.663] and

[ITU-T G.650.2]). Typical values vary with the implementation. The test methods for non-linear

coefficient remain under study.

I.5 Tables of common typical values

The values in Tables I.1 and I.2 are representative of concatenated optical fibre links according to

clauses I.1 and I.3, respectively. The implied fibre induced maximum DGD values in Table I.2 areintended for guidance with regard to the requirement for other optical elements that may be in

the link.

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Rec. ITU-T G.654 (10/2012) 13

Table I.1 – Representative value of a concatenated optical fibre link


Attenuation coefficient Wavelength Typical link value (Note)

1550 nm 0.25 dB/km

1625 nm To be determined

Typical dispersion coefficient D1550

S1550

To be determined

To be determined

NOTE – Typical link value corresponds to the link attenuation coefficient used in [b-ITU-T G.957]

and [b-ITU-T G.691].

Table I.2 – Differential group delay

Maximum PMDQ

(ps/ km)

Link length

(km)

Implied fibre induced

maximum DGD

(ps)

Channel bit rates

No specification Up to 2.5 Gbit/s

0.5 400 25.0 10 Gbit/s

40 19.0 (Note) 10 Gbit/s

2 7.5 40 Gbit/s

0.20 3000 19.0 10 Gbit/s

80 7.0 40 Gbit/s

0.10 > 4000 12.0 10 Gbit/s

400 5.0 40 Gbit/s

NOTE – This value applies also for 10 Gigabit Ethernet systems.

NOTE – Cable section length is 10 km except for the 0.10 ps/√km/> 4000 km link where, if set to 25 km, the

probability level is 6.5 × 10 –8

.

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14 Rec. ITU-T G.654 (10/2012)

Bibliography

[b-ITU-T G.652] Recommendation ITU-T G.652 (2009), Characteristics of a single-mode

optical fibre and cable.

[b-ITU-T G.663] Recommendation ITU-T G.663 (2011), Application related aspects of optical

amplifier devices and subsystems.

[b-ITU-T G.691] Recommendation ITU-T G.691 (2006), Optical interfaces for single channel

STM-64 and other SDH systems with optical amplifiers.

[b-ITU-T G.692] Recommendation ITU-T G.692 (1998), Optical interfaces for multichannel

systems with optical amplifiers.

[b-ITU-T G.957] Recommendation ITU-T G.957 (2006), Optical interfaces for equipments

and systems relating to the synchronous digital hierarchy.

[b-ITU-T G.959.1] Recommendation ITU-T G.959.1 (2012), Optical transport network physical

layer interfaces.

[b-ITU-T G.973] Recommendation ITU-T G.973 (2010), Characteristics of repeaterless

optical fibre submarine cable systems.

[b-ITU-T G.973.1] Recommendation ITU-T G.973.1 (2009), Longitudinally compatible DWDM

applications for repeaterless optical fibre submarine cable systems.

[b-ITU-T G.973.2] Recommendation ITU-T G.973.2 (2011), Multichannel DWDM applications

with single channel optical interfaces for repeaterless optical fibre

submarine cable systems.

[b-ITU-T G.977] Recommendation ITU-T G.977 (2011), Characteristics of optically amplified

optical fibre submarine cable systems.

[b-IEC 60794-2-11] IEC 60794-2-11 (2005), Optical fibre cables – Part 2-11: Indoor cables –

Detailed specification for simplex and duplex cables for use in premises

cabling.

[b-IEC/TR 61282-3] IEC/TR 61282-3 (2006), Fibre optic communication system design guides –

Part 3: Calculation of link polarization mode dispersion.

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SERIES OF ITU-T RECOMMENDATIONS

Series A Organization of the work of ITU-T

Series D General tariff principles

Series E Overall network operation, telephone service, service operation and human factors

Series F Non-telephone telecommunication services

Series G Transmission systems and media, digital systems and networks

Series H Audiovisual and multimedia systems

Series I Integrated services digital network

Series J Cable networks and transmission of television, sound programme and other multimedia signals

Series K Protection against interference

Series L Construction, installation and protection of cables and other elements of outside plant

Series M Telecommunication management, including TMN and network maintenance

Series N Maintenance: international sound programme and television transmission circuits

Series O Specifications of measuring equipment

Series P Terminals and subjective and objective assessment methods

Series Q Switching and signalling

Series R Telegraph transmission

Series S Telegraph services terminal equipment

Series T Terminals for telematic services

Series U Telegraph switching

Series V Data communication over the telephone network

Series X Data networks, open system communications and security

Series Y Global information infrastructure, Internet protocol aspects and next-generation networks

Series Z Languages and general software aspects for telecommunication systems

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